Two-way signaling system



Feb. 18, 1930. R. c. MATHES 1,747,835

TWO-WAY SIGNALING SYSTEM Filed Dec. 6. 1927 /NVENTOR ROBERT 6? MA THES BY W M Arr RNEY Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE ROBERT C. MATHES, OF WYOMING, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK TWO-WAY SIGNALING SYSTEM Application filed December 6, 1927. Serial No. 238,046.

This invention relates to signaling systems and methods of operation and more particularly to two-way signaling systems employing preferably Waves of the same carrier frequency for transmission in both directions.

Arrangements have heretofore been proposed for operating signaling systems in both directions in which voice operated relays control the sending and receiving apparatus. There is disclosed in U. S. Patent 1,691,076 issued November 13, 1928, to me, a voice operated control system for two-way radio signalin g systems in which the relays controlling the sending and receiving circuits are energized by voice currents.

An object of the invention is to provide improved methods of and apparatus for operating a two-directional carrier transmission system in which the same carrier frequency is used for transmission in both directions.

Another object of the invention is to provide switching means which are operated under control of the signals and which are positive in their operation and are of simplified and relatively inexpensive construction.

A feature of the invention is that the carrier wave from the sending station is utilized to energize the switching means at the receiving station. This use of the carrier wave provides the maximum initial energy for operating a switch at the receiving end as compared with the slowly rising energy which would be supplied by some types of signals especially speech as delivered by the demodulater.

In the specific embodiment of this invention herein shown and described a voice operated control system similar to that disclosed in the copending application referred to above is used except that the receiving channel is put in operative condition by the carrier currents Which are transmitted along with the side band energy due to the voice currents. Part of the voice currents at the sending end of the line are transmitted through an amplifier-rectifier to operate a relay which disables the receiving apparatus at the sending end and also to operate another relay which renders operative the carrier current oscillator, permitting the oscil later current to pass through the modulator and over the line to the receiving station. At the receiving station this carrier current passes through an amplifier-rectifier and operates a relay which disables the transmitting apparatus in the receiving station and also operates a second relay which renders operative the receiving circuit at the receiving station. The two stations are then in condition to signal in one direction only. The rest of the voice currents from the sending end pass through a delay filter to the modulator, thus inducing side band currents which pass out over the line along with the carrier. This delay filter insures that the various switching functions at the sending end are completed and that the sending circuit as a whole is prepared for one-way transmission at or before the instant when the first part of the signal reaches the modulator. An additional delay circuit may be used in the receiving circuit to insure that the relays which disable the transmitting apparatus at the receiving end and render have operated before the signals reach the receiving apparatus and thus insure that the received signal is not clipped.

This second delay circuit need not, however, be as elaborate as those commonly used forperforming similar functions and in some cases may be omitted altogether since in accordance with the invention the carrier is used to operate the switching apparatus at the receiving end and the voice currents may be delayed at the sending end for a suflicient time after the carrier has been transmitted to insure the proper operation of the relays at the receiving station before side band currents reach the demodulator.

The invention will be better understood by reference to the following specification and accompanying drawings in which: 1

Fig. l represents in diagrammatic form the circuits of a two-way carrier current station;

Fig. 2 represents a radio antenna circuit which may be substituted for that portion of the current of F ig.' 1 to the-right of lines Since the terminal stations may be identical operative the receiving apparatus in construction it has been deemed suflicient to illustrate only one terminal, and in the following description the manner in which. signals are received at and transmitted from a distant station will be clear from reference to the single station shown.

In the particular system illustrated in Fig.

1 the transmitting system comprises the low frequency line LL, the delay circuit 1, the mo ulator 2, the oscillator 3 and the high frequency line HL, by which combination the signals from the low frequency line LL are used to modulate the current from oscillator 3, after which the modulated signal is transmitted over the high frequency line HL.

The delay circuit 1 may be a low pass filter as shown at ly in Fig. 11 of U. S. patent to Campbell No. 1,227 ,114, granted May 22, 1917, although a delay circuit is not required to have the characteristics of a filter, or it may be of the type shown in U. S. patent to A9r2n5old No. 1,565,302, granted December 15, l

The modulator 2 is of the type well known 25 in the art from which sqme of the unmodulated carrier component 18 transmitted along with the side bands.

The receiving stem comprises the high gfrequency line H the demodulator 4, the

R dela circuit 5 and the low frequency line LL y means of which the received signal waves from the high frequency line HL are detected to reproduce a signal frequency current which is transmitted through the delay 85 circuit to the low frequency line LL. The

delay circuit 5 may be like delay circuit 1 or it may be different and as explained later in connection with the switching system disclosed, delay circuit 5 may in some cases be omitted.

The low frequency portions of the transmitting circuit are connected to the common line LL, through a three-winding transformer T and network N by means of which the connection may be made substantially conugate.

he operation of the switching system is as follows: When the signal currents pass from the low frequency line LL, through transformer T, part of the signal current is shunted through an amplifier-rectifier 6 by a connection made at points in advance of delay circuit 1. The currents transmitted through this amplifier-rectifier operate rela s 7 and 9. Relay 7 actuates switch 8 whic is normally biased to the circuit closing position. Relay 9 actuates switch 10 away from its normal sition as shown, removing the short circuit from oscillator 3 and allowing the carrier wave to pass through modulator 2 and over-the high frequency line HL. Preferably, relay is adjusted to operate before relay 9 in order to disable the receiving circuit before the transmitting circuit is in condition to transmit the carrier currents. The

si al currents which pass through delay circuit 1 due to the time constant of this circuit, do not reach the modulator 2 until after relays 7 and 9 have operated.

As soon as switch 10 is opened by the operation of relay 9, the carrier currents, unmodulated by the signal currents, are transmitted over high frequency line HL to the receiving station. The action occurrin at the receiving station will be understood y considering the receiving side of Fig. 1. Part of the received carrier current, by connection made at points in advance of demodulator 4, is shunted through am lifier 11 to energize relays 12 and 13, there y actuating switches 14 and 15. Relay 12 is preferably adjusted to operate before relay 13 so that switch 14 will disconnect the sending circuit from transformer T before switch 15 removes the short circuit from the receiver.

The sending and receiving stations are then in condition for transmission in one direction onl The time of transmission through the delay circuit 1 is so chosen that the signaling currents will not reach the input side of modulator 2 until the means for putting the sending circuit in operative condition have been 0 rated by relays 7 and 9. Similarly, upon t e termination of a signal the time'lag of the relays may be such that the transmitting station 1s not rendered inoperative until the last part of the signal has traversed the delay circuit and has been transmitted "by the modulator. Likewise, the time of transmission of delay circuit ii is so chosen that the signaling currents will not reach the input si e of transformer T at the receiving station until the means for putting the receiving circuit at the receiving station in operatlve condition have been operated by relays 12 and 13. The time lag of these relays is so chosen that the receiving station is not rendered inoperative for receiving until the last part of the signal has traversed the delay circuit 5 and transformer T to the low frequency line LL.

Obviously, since the means for putting the receivin circuit at the receiving station are operate by the carrier currents by means of a connection in advance of modulator 4, if delay circuit 1 has a sufliciently large time constant so that the signal modulated currents do not reach the demodulator until after the means for putting the "receiving. circuit at the receiving station in oflierative condition have been operated by re ays 12 and 13, delay circuit 5 can be omitted.

Since both the sending and receiving stations are never in condition to transmit at the same time singing of the ap aratus is impossible and it is also impossl Is for a signal current being transmitted in one directionto be reflected back to the receiver of the sending station.

Fig. 2 illustrates a radio antenna circuit whic I may be substituted for that portion of the circuit shown in Fig. 1 to the right of lines X-X for utilizing the-invention in connection with a two-way radio signaling system in which the carrier is transmitted along with the side bands. Antenna AN which is normally biased by means, not shown, to its receive position is switched to its transmitting position by relay 16 which actuates switch 17. Relay 16 is in the transmitting control circuit and connected to amplifier-rectifier 6. In the connection shown relay 16 is in the-energizing circuits of relays 7 and 9, and is actuated simultaneously with them. v

While the one embodiment of the invention has been shown and described in detail, it is to be understood that the invention is generic in character and is not to be construed as limited to this particular embodiment since numerous modifications'thereof may be made by persons skilled in the art without departing from the spirit of the applicants invention, the scope of which is to be determined by the appended claims.

What is claimed is:

1. A two-way signaling systemcomprising a sending station, a normally inoperative receiving circuit,,me'ans at the sending station for transmitting a signal modulated car rier wave, and means operative during the transmission of said wave' for rendering said receiving circuit operative to receive, said last means being controlled by the unmodulated carrier wavefrom the sending station.

2. In a two-way signaling system for transmitting modulated carrier waves of the same frequency in both directions, sending stations and normally inoperative receiving stations, means associated with said system to render said receiving station operative for one way transmission in response to transmitted waves and to restore the system to its normal condition when the transmitted waves cease, said means at the receiving station being responsive to the carrier waves from the sending station, and means to delay the transmission of signals until after the-carrier waves have been applied to the sending circuit.

3. In combination, a line, sending and receiving apparatus associated therewith, employing carrier waves for telephonic trans mission, voice operated relays for controlling the sending apparatus, and carrier operated relays for controlling the receiving apparatus, said carrier operated relays being rendered operative by the unmodulated carrier currents. 1

4. A signaling system comprising a plurality of sending and receiving stations, said receiving stations being normally disabled, means at said receiving stations for putting the receiving apparatus in condition to receive, said last means being actuated in response to the unmodulated carrier currents transmitted from a sending station.

5. The method of operating a two way carrier signaling system in which a transmitting and a receiving channel are provided at each ofthe two intercommunicating stations and the carrier is transmitted from a modulater along with the side band which comprises putting the source -of carrier current at one of said stations in condition for transmitting in response to signal currents from said station, delaying the arrival of said signal currents at said modulator, and putting the receiving channel at the. other ofsaid stations in condition to receive in response to the unmodulated carrier currents from said first mentioned station'before said signal currents from said last mentioned station arrive at said modulator at said first mentioned station.

6. In combination, a source of electrical impulses, a source of carrier current, means for modulating'said carrier current by said electrical impulses, means for delaying the arrival of said electrical impulses at said modulating means, a high'fi'equency line over i 'by said unmodulated carrier currents for controlling the effective connection of said low frequency line at the receiving station with said high frequency line.

8. In a two-way signaling systeincompris ing a normally inoperative receivingcrrcult, means at a sending station for transmitting a signal modulated carrier wave, means at said sending station for delaying the transmission of the signal current to the modulating means, means actuated in response to the unmodulated carrier currents, said means remaining actuated in response to the modulated-carrier currents, for rendering said receiving circuit operative to receive, and means for restoring said receiving circuit to its 1n-. operative condition upon the failure of the said carrier current.

9. In a telephone system, the combination of a transmitting device, a receiving device, a high frequency circuit, said transmitting device including a source of carrier current oscillations and a modulator, said transmitting device having "associated therewith transmittin 4o rent oscillations are means for putting said oscillator in condition 5 toreceive in response to said modulated carrier currents.

10. In a high frequency signaling system comprising telephone transmitting and receiving stations, said transmitting station com rising a generator of carrier frequency osci ations, means for modulatin said carrier oscillations in accordance wit said signal oscillations, said receivin station bein normally inoperative, means or putting-said receiving station in'condition for operation, said last means being controlledby the reception of said unmodulated carrier frequency oscillations.

-11. In a signaling system, a plurality of terminal stations each comprising a line adapted to transmit telephonic currents, a modulated carrier current telephone trans: mitting and receiving system associated with said line, and control means, each of said transmitting systems comprisin' a source of carrier currents, means for mogulatin said carrier currents in accordance with sai telephonic currents, and means for transmitting said modulated and unmodulated oscillations, each of said receivin systems comprising means for receiving t e unmodulated and modulated oscillations transmitted from another station and -means for demodulating the reccived'modulated oscillations, said control means comprising means actuated in response to the unmodulated oscillations received from said other station for preventing the transmission of oscillations from the local system 7 while. the carrier ourbeing received from said other station. i

12. In a signaling system, a plurality of terminal stations each comprising a .line to transmit telephonic currents, a modulated 46 carrier cur-rent telephone transmittin and receiving system associated with sai line, andcontrol means, each of said transmitting systems comprising a source of carrier currents mea ns for modulating said carrier cur- 50 rents in accordance with said telephonic curtion to transmit and said local receiving sys-V tem disabled, means responsive to unmodu lated carrier currents transmitted from another station for putting said receiving system in condition to receive and for revent- .ing the transmission'of oscillations rom the local transmitting s stem while carrier current oscillations are ein received from said other station, and a di said demodulator and said line for dela ing the transmission of telephonic currents rom said demodulator to said line until said receiving system is in condition to receive and said local transmitting system disabled.

13. A signal transmission system comprising means to transmit a signal-modulated carrier wave containing an unmodulated carrier component, a normally inoperative receiving station, a signal receiving circuit thereat, means controlled by the unmodulated carrier component for renderin the receiving station operative to receive signals, and signal storing means-in advance of the signal receiving circuit for permitting the receivingcircuit to be put into operative condition before initial portions of the si al modulated carrier wave are impresse uponsaid 1 signal receiving circuit.

14. A two-way signalingstation for a carrier transmission channel, including a trans mittin branch and a receiving branch, both norma ly inoperative, means responsive to impressed signals for rendering the transmitting branch operative to transmit signal controlled carrier waves over the channel and means responsive to unmodulated carrier ay circuit between wave components received from said channel to render said receiving branch operative to receive signals from said carrier channel In witness whereof, I hereunto subscribe my name this 3rd day of December, A. D.

ROBERT c. MATHES.

rents, m'eansfor transmitting said unmodulated and modulated osci tions, each of said rece vin systems comprising means for receiving t e modulated'oscillations transmit- $5 ted from another station and. means comprising a demodulator for-det'ectin the reoeived modulated oscillations, sai control means comprisin means res nsive to telephonic currents said line to said transmitting system, a delay in said hne for. putting said transmitting system in condition to 

